2. Warm-up- hand this in for credit
1. Define evolution
2. Define natural selection.
3. What are the four components that are important in order for natural selection to occur?
4. The Hardy-Weinberg equilibrium equation is used to make predictions of allelic and genotypic frequencies for future generations. If a population in a future generation has allelic frequencies that do not match the predicted values, what does this mean?
5. You encounter a population in which there are 100 individuals. 25 of these individuals are homozygous dominant.
A) what is the allele frequency for this dominant allele?
B) What proportion of the next generation’s population should be heterozygous?

3. Evolution Change in allele frequencies in populations over time OR
Change in genetic composition in a population from generation to generation (or over time)

4. Natural selection
Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals without those traits

5. Key component of natural selection!! You must know this!!
1. Individuals in a population vary in traits
2. These traits must be heritable
3. Species can produce more offspring than their environment can support
4. Species with certain traits survive and reproduce at higher rates than those without those traits
*Individuals do not evolve!! Only populations do!
*Natural selection acts on individuals and leads to adaptive evolution!

6. You encounter a population in which there are 100 individuals
You encounter a population in which there are 100 individuals. 25 of these individuals are homozygous dominant. A) what is the allele frequency for this dominant allele? B) What proportion of the next generation’s population should be heterozygous?

7. Homework
1) Page 491
List each type of reproductive barrier, explain it, and give an example. Due tomorrow
2) Read pp
3) essay #1 due this Thursday
Typo!!!! Recheck the updated version!!!!!

8. The key component for evolution to occur is…
Genetic variation!!

9. Genetic Variation
Genetic variation among individuals is caused by differences in genes or other DNA segments
Phenotype is the product of inherited genotype and environmental influences
Natural selection can only act on variation with a genetic component

10. Variation Within a Population
Both discrete and quantitative characters contribute to variation within a population
Discrete characters can be classified on an either-or basis
Example: color, shape, presence/absence of a phenotype
Quantitative characters vary along a continuum within a population
Example: body mass, litter size
Discrete: color
Quantitative: size

11. Sources of Genetic Variation
New genes and alleles can arise by mutation or gene duplication
Sexual reproduction produces genetic variation through crossing over, independent assortment, and fertilization

12. Alleles are different variations of a gene
Genotypes are combination of alleles that an individual has,
One allele came from parent 1, and other came from parent 2

13. Hardy-Weinberg Principle
Allele frequencies of alleles and genotypes in a population will remain constant from generation to generation if all assumptions are met
A gene pool that remains constant is said to be in Hardy- Weinberg equilibrium

14. AA Aa aa ?
Generation 1
Generation 2

15. AA Aa aa ?
Generation 1
Generation 2
p2 + 2pq + q2 = 1

16. Practice on your own : Write this in your notes.
What are the genotypic frequencies?
What are the allelic frequencies?
If there are 700 cats in the next generation, how many of them should be homozygous recessive in the next generation? (assume HW equilibrium)

18. Cystic Fibrosis 1
The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers?
about 0.04%
about 2%
about 4%
The frequency cannot be calculated because selection violates Hardy- Weinberg assumptions.
Answer: c
The frequency of carriers is 2pq. The allele frequency, q, is 1/50 since qq = 1/2500. P is close to 1. You may want to discuss why option d does not apply. 18

19. Cystic Fibrosis 1
The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers?
about 0.04%
or about 2%
or about 4%
The frequency cannot be calculated because selection violates Hardy- Weinberg assumptions.
Answer: c
The frequency of carriers is 2pq. The allele frequency, q, is 1/50 since qq = 1/2500. P is close to 1. You may want to discuss why option d does not apply. 19

20. Assumptions of Hardy-Weinberg principle
Allele frequencies in a population will remain constant if ALL of the following conditions are met:
The population is infinitely large
Individuals mate randomly
No genetic migration
No natural selection
No mutation

21. Three main driving forces that cause changes in allele frequencies
Natural selection
Genetic drift
Gene flow

22. 1) Natural selection
Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals without those traits
Adapations are inherited traits that enhance organismal survival and reproduction in specific environments
Fitness: measure of reproductive success associated with a particular trait

23. Natural selection is the only mechanism that consistently causes adaptive evolution
Evolution by natural selection involves both chance and “sorting”
New genetic variations arise by chance
Beneficial alleles are “sorted” and favored by natural selection
Only natural selection consistently results in adaptive evolution

24. Types of natural selection
Directional
Disruptive
Stabilizing

25. Frequency of individuals
Figure 23.13
Original population
Frequency of
individuals
Phenotypes (fur color)
Original
population
Evolved
population
Figure Modes of selection.
(a) Directional selection
(b) Disruptive selection
(c) Stabilizing selection

26. 2) Genetic Drift- the reason why large population size is important for Hardy-Weinberg Equilibrium
The smaller a sample, the greater the chance of deviation from a predicted result
Genetic drift : when chance events cause allele frequencies to fluctuate unpredictably from one generation to the next
Genetic drift tends to reduce genetic variation through losses of alleles

27. Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 CRCR
Figure
CRCR
CRCR
CRCW
CWCW
CRCR
CRCW
CRCR
CRCW
Figure 23.9 Genetic drift.
CRCR
CRCW
Generation 1
p (frequency of CR) = 0.7
q (frequency of CW) = 0.3

28. 5 plants leave off- spring
Figure 5
plants
leave
off-
spring
CRCR
CRCR
CWCW
CRCR
CRCW
CRCW
CWCW
CRCR
CRCR
CWCW
CRCW
CRCW
CRCR
CRCW
CWCW
CRCR
Figure 23.9 Genetic drift.
CRCR
CRCW
CRCW
CRCW
Generation 1
Generation 2
p (frequency of CR) = 0.7
p = 0.5
q (frequency of CW) = 0.3
q = 0.5

29. 5 plants leave off- spring 2 plants leave off- spring
Figure 5
plants
leave
off-
spring 2
plants
leave
off-
spring
CRCR
CRCR
CWCW
CRCR
CRCR
CRCW
CRCW
CRCR
CRCR
CWCW
CRCR
CRCR
CWCW
CRCR
CRCR
CRCW
CRCW
CRCR
CRCR
CRCR
CRCW
CWCW
CRCR
CRCR
Figure 23.9 Genetic drift.
CRCR
CRCW
CRCW
CRCW
CRCR
CRCR
Generation 1
Generation 2
Generation 3
p (frequency of CR) = 0.7
p = 0.5
p = 1.0
q (frequency of CW) = 0.3
q = 0.5
q = 0.0

30. The Founder Effect
The founder effect occurs when a few individuals become isolated from a larger population. Example: wind blows birds off course to another island
Allele frequencies in the small founder population can be different from those in the larger parent population

31. The Bottleneck Effect
The bottleneck effect is a sudden reduction in population size due to a change in the environment , ex: urbanization
The resulting gene pool may no longer be reflective of the original population’s gene pool
If the population remains small, it may be further affected by genetic drift

32. Figure
Figure The bottleneck effect.
Original
population

33. Original population Bottlenecking event
Figure
Figure The bottleneck effect.
Original
population
Bottlenecking
event

34. Reduction in genetic variation via genetic drift!!!
Figure
Reduction in genetic variation via genetic drift!!!
Figure The bottleneck effect.
Original
population
Bottlenecking
event
Surviving
population

35. Case Study: Impact of Genetic Drift on the Greater Prairie Chicken
Loss of prairie habitat caused a severe reduction in the population of greater prairie chickens in Illinois
The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched

36. Greater prairie chicken
Figure 23.11
Pre-bottleneck
(Illinois, 1820)
Post-bottleneck
(Illinois, 1993)
Greater prairie chicken
Range
of greater
prairie
chicken
(a)
Number
of alleles
per locus
Percentage
of eggs
hatched
Population
size
Location
Illinois
1930–1960s
1993
1,000–25,000
<50
5.2
3.7 93
<50
Figure Genetic drift and loss of genetic variation.
Kansas, 1998
(no bottleneck)
750,000
5.8 99
Nebraska, 1998
(no bottleneck)
75,000–
200,000
5.8 96
(b)

37. Effects of Genetic Drift: A Summary
Genetic drift is significant in small populations
Genetic drift causes allele frequencies to change at random
Genetic drift can lead to a loss of genetic variation within populations
Genetic drift can cause harmful alleles to become fixed

38. 3) Gene Flow
Gene flow consists of the movement of alleles among populations
Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen)
Gene flow tends to reduce variation among populations over time
Gene flow can decrease or increase the fitness of a population